Ultrasonic instruments that use multi-element phased array transducers provide higher inspection efficiency compared to instruments using only single element transducers. As is well known by those skilled in the art, a stationary phased array transducer can cover a larger inspection region than a stationary single element transducer because the phased array transducer emission beam axis can be electronically steered to cover a two-dimensional sector area, or three-dimension volume, by applying successive pulse-receive cycles with different focal laws—i.e. performing an S scan. Single element transducers are only capable of emission along a single beam axis.
Furthermore, when performing inspections requiring only a single beam axis (i.e. A scan), a single element transducer requires the fastening and removal of a specific angle wedge to cover more than one incident beam angle; whereas, the phased array transducer can change the incident angle electronically.
Accordingly, the single element transducer inspection method is less efficient because it requires the operator to physically move, or otherwise adjust and modify, the transducer in order to cover the same area, or range of beam angles, that a phased array transducer can in a stationary position.
There are, however, significant problems associated with conventional phased array instruments concerning inefficient detection of faulty elements and their effect on measurement data accuracy.
Ultrasonic phased array transducers are comprised of an array of small sensor elements, each of which can be pulsed individually in accordance with focal laws to steer and focus excitation signals, and focus reception signals. The response signals from multiple elements of a phased array transducer are summed together to produce an A scan for analysis and sector, or linear, scan image rendering. If one or a few elements are faulty, there will be an error in the summed response; however, the error may be difficult to discern because it is only a small part of the total sum. A faulty single element transducer does not have this problem because it is the sole signal source for the observed A-scan; therefore, unexpected signal responses can be easily discerned.
The term ‘faulty’ in the present disclosure is defined as an element having little or no response to an incident echo signal as compared to neighboring non-faulty elements.
The accuracy and efficiency of the phased array inspection process is of high importance because costly repair and maintenance decisions are made based on the presumed accuracy of the measurement data, and the cost associated with the inspection itself can be substantial. Accordingly, performing these inspections without being aware of the presence of a faulty element, or elements, can have a significant unfavorable effect on the validity of the inspection measurement data.
Conventional solutions for detecting faulty elements exist; however, they employ time consuming calibration processes that require the inspection process to cease when conducted, thereby reducing efficiency.
Another solution that is taught in U.S. Pat. No. 5,572,219 discloses a method and apparatus that generates calibration data for each element of a phased array transducer by comparing the reading from each transducer element when a calibration is applied with a set of predetermined data that is expected to be obtained for each element.
The problem with this and other existing calibration technologies is that complete calibrations of phased array instruments are not performed on a frequent basis; therefore, the transducer performance is not monitored between calibration sessions.
It would therefore be beneficial to provide a simple and systematic method for automatic detection of faulty phased array transducer elements on a continuous basis without unfavorable impact on the accuracy or efficiency of the inspection process.
It should be noted that the advantages of the present disclosure can also be applied to phased array measurements methods other than the S scan, such as, but not limited to, linear scans and dynamic depth focusing.